1. Field of the Invention
The invention herein relates to a method for supplying sensible heat to a chemical conversion process, and particularly to a process and system for the production of an olefin, more particularly to a process and system for the production of styrene by means of the dehydrogenation of ethylbenzene.
2. Description of the Related Art
The production of styrene by the catalytic dehydrogenation of ethylbenzene is well known in the art. Typically, a feed containing steam and ethylbenzene is contacted with a catalyst in a reactor at an inlet temperature of from about 600° C. to about 650° C. to effect conversion. Steam is heated to a predetermined temperature in a steam superheater. The steam supplies at least some of the heat needed for the reaction and, as a diluent, reduces the partial pressure of the styrene and hydrogen, thereby shifting the reaction equilibrium towards the production of styrene.
U.S. Pat. No. 4,628,136 to Sardina discloses a dehydrogenation process for the production of styrene from ethylbenzene in the presence of steam. Ethylbenzene and water form an azeotropic mixture which boils at a lower temperature than either ethylbenzene or water. Most of the ethylbenzene/water feed is vaporized by condensing overhead vapor from the ethylbenzene/styrene splitter system. This feature saves energy since less steam needs to be used to vaporize the feed stream and less cooling water is required to condense the overhead vapor of the ethylbenzene/styrene splitter
The mass steam to oil ratio, i.e., the ratio of steam to ethylbenzene contained in a feedstream (“oil”) on a weight basis, is an important factor in the dehydrogenation of ethylbenzene. In the past, styrene production plants operated at overall steam/oil weight ratios of 1.3 to 1.7. Improved catalysts have allowed the process to operate at steam/oil weight ratios of about 1.0 with acceptable reductions in yield or ethylbenzene conversion.
To supply the proper amount of heat to the system at an overall steam/oil weight ratio of 1.0 or lower, the temperature at the outlet of the steam superheater would have to be increased to 950° C. or even higher. However, superheater temperatures above 927° C. require the use of special and costly metallurgy. It would be advantageous to have a system which operates at both low steam/oil ratios and lower temperatures.